Denver International Airport’s several new concourses are now fully enclosed after construction crews finished the outer walls.

The completion of the outer walls of Concourses A-West, B-East and C-East marks an important milestone for the airports Gate Expansion Program.

In addition to the outer walls being finished, a “curtain wall” system has been installed in all three expansion areas that is a wall of windows of varying opacity, which will allow more light into the new areas, while decreasing energy costs, according to a release from the airport.

“We are so grateful to the hard-working teams who have successfully continued progress on this exciting program through the challenges of the pandemic,” said Stu Williams, senior vice president of airport expansion at DIA in a release. “This program will accommodate current and future growth at DEN with additional gate capacity, new passenger amenities and opportunities for our airline partners to grow in Denver.”

The Gate Expansion Program will add 39 gates to the airport, which will increase capacity by 30%. Construction began in the summer of 2018, and last last year. according to a release.

DIA has opened the first four gates on Concourse B-West, which allowed passengers to get a glimpse of what is too come.

Williams said the expansion is expected to be fully complete next year.